Spectral uniformity of two- and four-level diffractive optical elements for spectroscopy

Hallvard Angelskår,Ib-Rune Johansen,Aasmund S Sudbø,Håkon Sagberg,Matthieu Lacolle

doi:10.1364/oe.17.010206

Abstract

We present simulations and characterization of gold coated diffractive optical elements (DOEs) that have been designed and fabricated in silicon for an industrial application of near-infrared spectroscopy. The DOE design is focusing and reflecting, and two-level and four-level binary designs were studied. Our application requires the spectral response of the DOE to be uniform over the DOE surface. Thus the variation in the spectral response over the surface was measured, and studied in simulations. Measurements as well as simulations show that the uniformity of the spectral response is much better for the four-level design than for the two-level design. Finally, simulations and measurements show that the four-level design meets the requirements of spectral uniformity from the industrial application, whereas the simulations show that the physical properties of diffraction gratings in general make the simpler tw level design unsuitable.

Highlights

A diffractive optical element (DOE) can perform several key functions in optical instruments such as beam splitting, focusing and filtering
We present simulations and characterization of gold coated diffractive optical elements (DOEs) that have been designed and fabricated in silicon for an industrial application of near-infrared spectroscopy
The height of the two-level DOE surface profile was determined taking into account all the five wavelengths, giving a maximal height of h2 = λavg/2 ≈ 424 nm

Summary

Introduction

A diffractive optical element (DOE) can perform several key functions in optical instruments such as beam splitting, focusing and filtering. DOEs can replace conventional optical components that perform these functions, promising several advantages such as small footprint, low weight and low cost. Several micro-spectrometer designs with DOEs have been suggested recently, such as [1] and [2], taking advantage of these possibilities. Silicon processing facilitates integrated optical microspectrometers, as reviewed in [3]. In an earlier report from our research group, the design of focusing diffractive optical elements for spectroscopy applications in the near-infrared was described [4]. Quantitative spectroscopy is a very demanding application for a DOE, requiring the fabricated DOE surface to match the design very closely, with submicron accuracy

Results

Discussion

Conclusion